From 4278afcbc4e07742e3901e412463f8d6efeba2ce Mon Sep 17 00:00:00 2001
From: Ian Gulliver <github@flamingcow.io>
Date: Tue, 25 Apr 2023 15:18:35 -0700
Subject: [PATCH] Working two-way proxy

---
 go.sum   |  0
 proxy.go | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 83 insertions(+), 4 deletions(-)
 create mode 100644 go.sum

diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..e69de29
diff --git a/proxy.go b/proxy.go
index c51d237..7e0df0b 100644
--- a/proxy.go
+++ b/proxy.go
@@ -1,17 +1,28 @@
 package proxy
 
-import "net"
+import (
+	"errors"
+	"net"
+	"sync"
+	"testing"
+)
 
 type Proxy struct {
+	t        *testing.T
 	backend  *net.TCPAddr
 	listener *net.TCPListener
+
+	conns map[*net.TCPConn]bool
+	mu    sync.Mutex
 }
 
-func NewProxy(backend *net.TCPAddr) (*Proxy, error) {
+func NewProxy(t *testing.T, backend *net.TCPAddr) (*Proxy, error) {
 	var err error
 
 	p := &Proxy{
+		t:       t,
 		backend: backend,
+		conns:   map[*net.TCPConn]bool{},
 	}
 
 	p.listener, err = net.ListenTCP("tcp", nil)
@@ -21,20 +32,88 @@ func NewProxy(backend *net.TCPAddr) (*Proxy, error) {
 
 	go p.accept()
 
+	t.Logf("* -> %s -> [proxy] -> * -> %s listening...", p.listener.Addr(), p.backend)
+
 	return p, nil
 }
 
+func (p *Proxy) Addr() *net.TCPAddr {
+	return p.listener.Addr().(*net.TCPAddr)
+}
+
 func (p *Proxy) Close() {
+	p.t.Logf("* -> %s -> [proxy] -> * -> %s closing...", p.listener.Addr(), p.backend)
+
 	p.listener.Close()
+
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	for conn := range p.conns {
+		conn.Close()
+	}
+
+	p.conns = map[*net.TCPConn]bool{}
+
+	p.t.Logf("* -> %s -> [proxy] -> * -> %s closed", p.listener.Addr(), p.backend)
 }
 
 func (p *Proxy) accept() {
 	for {
-		conn, err := p.listener.Accept()
+		frontConn, err := p.listener.AcceptTCP()
 		if err != nil {
 			return
 		}
 
-		conn.Close()
+		go p.dial(frontConn)
+	}
+}
+
+func (p *Proxy) dial(frontConn *net.TCPConn) {
+	p.t.Logf("%s -> %s -> [proxy] -> * -> %s dialing...", frontConn.RemoteAddr(), frontConn.LocalAddr(), p.backend)
+
+	backConn, err := net.DialTCP(p.backend.Network(), nil, p.backend)
+	if err != nil {
+		p.t.Logf("%s -> %s -> [proxy] -> * -> %s dialing failed: %s", frontConn.RemoteAddr(), frontConn.LocalAddr(), p.backend, err)
+		frontConn.Close()
+		return
+	}
+
+	p.t.Logf("%s -> %s -> [proxy] -> %s -> %s connected", frontConn.RemoteAddr(), frontConn.LocalAddr(), backConn.LocalAddr(), backConn.RemoteAddr())
+
+	p.addConns(frontConn, backConn)
+
+	go p.copy(frontConn, backConn)
+	go p.copy(backConn, frontConn)
+}
+
+func (p *Proxy) copy(src, dest *net.TCPConn) {
+	numBytes, err := dest.ReadFrom(src)
+
+	if err == nil || errors.Is(err, net.ErrClosed) {
+		p.t.Logf("%s -> %s -> [proxy] -> %s -> %s closed after %d bytes", src.RemoteAddr(), src.LocalAddr(), dest.LocalAddr(), dest.RemoteAddr(), numBytes)
+	} else {
+		p.t.Logf("%s -> %s -> [proxy] -> %s -> %s closed after %d bytes: %s", src.RemoteAddr(), src.LocalAddr(), dest.LocalAddr(), dest.RemoteAddr(), numBytes, err)
+	}
+
+	dest.Close()
+	p.delConns(src)
+}
+
+func (p *Proxy) addConns(conns ...*net.TCPConn) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	for _, conn := range conns {
+		p.conns[conn] = true
+	}
+}
+
+func (p *Proxy) delConns(conns ...*net.TCPConn) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	for _, conn := range conns {
+		delete(p.conns, conn)
 	}
 }